Apparatus and processes are known where a tube of plastic wrap is continuously fed through a bag forming, filling and sealing apparatus. Initially the bottom or leading edge of the bag or package is sealed and a suitable volume and weight of goods is deposited into the tube. Such goods may include noodles, peanuts, aluminum washers or the like. Then the tube is sealed above the top of the goods and the package is severed from the continuously moving tube.
It is conventional for sealing jaws to seal the top of the package while simultaneously forming an adjacent seal which comprises the bottom of the next following container. Inherently air is trapped in the package in the head space between the goods and the top seal. The problem which exists in the industry is how to deflate the gas impermeable package to reduce the package volume prior to the time it is sealed.
It will be self-evident that a pound of aluminum washers will pull the sidewalls of the container toward each other and thereby create a much smaller volume of air in the head space than will a one pound batch of spirally-wound egg noodles. The geometric shape of the washers is such that the washers align with each other and take up a small volume of space. On the other hand, the egg noodles are wound in a fashion to make up a much larger geometric shape and thereby the radial bulge of the plastic packaging will be greater.
It is not just that the air is trapped in the package and creates a more bulky package. Evacuation of the air from the package is important even where the excess bulk is acceptable. In some instances the goods within the package are susceptible to deterioration when exposed to relatively large volumes of gases as may be in a sample of air. By way of example, some foods such as cheese tend to oxidize or mold over a period of time if sufficient oxygen is contained within the package.
Industry has recognized the problem and three conventional operations are employed to solve it, that is, deflate the package to remove air.
One of the solutions for deflating packages is to puncture the package with small holes after the goods are sealed therein. The small holes allow the excess air within the package to be expelled by mechanical application of force or simply by the force of gravity settling the products during shipment and the like. However, this particular solution to the problem is unacceptable when foods are contained within the package. The pin holes used to allow the escape of trapped air also allow the ingress of contaminates from outside the package.
Another solution provided by the industry is a vacuum drawn on the inside of the package or container through the fill opening. The vacuum will extract the excess air or other gas and collapse the plastic sidewalls just prior to the sealing of the opening. This is a perfectly satisfactory solution in some instances. However, use of this system will slow the process due to the time required to evacuate gas from the fill tube. These systems also require the installation of equipment within the fill tube to close the tube off from the atmosphere. This additional equipment reduces the tube diameter which may cause plugging due to product bridging.
A third solution to the package deflation problem is to provide mechanical force directly to the outside of the package immediately before the sealing takes place and examples of this are sponge rubber or coiled springs which engage the outside of the package to expel excess air immediately prior to the time the sealing jaws engage and seal the fill opening. This will work with limited success and does not create a problem of contamination of the goods within the package. However, the heat of the sealing jaws and the often irregular surfaces of the goods within the package tend to cause uneven wear of the foam rubber and uneven elongation of the springs. As a result of the uneven wear and deterioration from the close proximity to the heated sealing elements, the long term manufacturing standards may not be maintained at the desired level. Additionally, fragile products such as potato chips are easily crushed by exterior mechanical applications of force. Also, density variations of the product cause changes in the product fill height and these changes can occur within a time span of a few minutes. When using mechanical deflators, correction of these changes requires a shutdown of the machine to modify the deflation force or position.